The Internet protocol (IP) is used to connect network nodes by routing data packets to IP addresses assigned to the nodes. IP addresses were traditionally associated with a fixed network location. Thus if a node moved from one location to another, a new IP address needed to be assigned to the node at the node's new location. That made roaming across networks difficult, as it was not possible to maintain the continuity of an Internet Protocol (IP) application session when a node changed its IP address. The Internet Engineering Task Force (IETF) therefore developed a standards based protocol called Mobile IP that enables a node to maintain a unique, fixed, home IP address even when the node moves from one network to another.
Mobile IP employs two IP addresses, a home IP address that remains constant wherever a node is located, and a “care-of” IP address that changes when a node moves to a new network. Using Mobile IP, a data packet intended for a roaming node is first received at the roaming node's home IP address. The data packet is then encapsulated by a Home Agent, which typically resides in a Customer Enterprise Network (CEN), and is tunneled to the care-of IP address. The data packet sourced by the mobile node from a foreign network is tunneled to the home agent which de-capsulates and forwards the data packet to the destination. Because its home IP address remains constant, such a roaming node is able to maintain the continuity of Internet Protocol (IP) application sessions even as the node moves across networks. In addition, to enable secure connectivity, the CEN may provide a Virtual Private Network (VPN) Server that uses a tunnel, for example using IPSec Encapsulating Security Payload-ESP protocol, to encrypt/de-crypt all communication to/from mobile nodes that have moved away from the CEN.
Mobile IP is sometimes used in combination with ad hoc and mobile networks. An ad hoc network is a collection of nodes that communicate by forming a multi-hop radio network without the need of infrastructure. Nodes in an ad hoc network forward information (e.g., frames) to other nodes by selecting one of the available routes to a destination node based on several parameters, such as link quality and round trip time. Generally ad hoc networks do not have a fixed topology. Nodes can dynamically join and leave an ad hoc network, and ad hoc networks can vary in degree of mobility. Further, an ad hoc network typically can heal itself by selecting alternate routes to a destination node when a first route is blocked, and thus each node in an ad hoc network can be viewed as a router. The dynamic formation of ad hoc networks, the ability to setup a network anywhere without the need of infrastructure, and the self healing characteristics make ad hoc networks useful in various situations, such as public safety incident scenes, where infrastructure connectivity might not be available.
In a mobile network, a mobile router provides connectivity to a group a hosts/routers connected to the mobile router. The hosts connected to a mobile router may share a home subnetwork with the mobile router (called home mobile nodes) or the hosts may have a different home subnetwork (called visiting mobile nodes). A mobile router typically uses mobile IP to receive packets from a home agent in the CEN and distribute packets to nodes connected to the mobile router's mobile network. A mobile router may have different levels of infrastructure connectivity (for example, connections to the CEN or connections only to a high risk building). A mobile router itself may be part of an ad hoc network. If a visiting node moves within range of an ad hoc network and seeks to transmit a data packet to a receiving node in the ad hoc network, a most efficient path for the data packet might be a single hop path including a direct peer to peer transmission of the data packet from the visiting node to the receiving node. However, if the visiting node is employing Mobile IP or a VPN, a Mobile IP or VPN application can force the visiting node to transmit the data packet to the receiving node through a much less efficient path. Such a less efficient path can include tunneling the data packet to the receiving node's Home Agent or VPN Server located in another network, and then transmitting the data packet from that network back to the receiving node.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.